Joint arthroplasty involves replacing articular cartilage with an implant that is intended to last as long as possible. The most common joints to replace are the knee and hip. Elbow and humerus replacements are the next most common. While it may be possible to also replace wrist and ankle bones with such an implant, are also possible to replace with an implant, effective treatments by fusion are still accepted and preferred by doctors and patients.
Initially reserved for patients suffering from arthritic conditions, hip and knee replacements have become increasingly popular especially for younger, more active individuals. As more of the “baby boomer” population requires joint arthroplasty, need for treating fractures and other joint conditions of the elderly will nearly double. There is also a growing secondary market for revision surgery products. The latter surgery carries a higher complication risk due to decreasing functional status of the patient with each intervention and with higher occurrences of infection, in part, due to the usual multi-stage nature of such surgeries and due to the fact that an antibiotic regimen alone is usually insufficient for curing same. Many of these infections are due to the general behavior of biofilm bacteria, i.e., the pathologic organisms that form colonies on inert surfaces. The best treatment for such situations is a total purging/removal of the infected area.
Joint replacements, being made of an inert material, provide excellent surfaces on which bacteria may colonize. Once a joint gets infected, general treatment involves completely removing the prior implant (itself, a rather risky procedure), followed by wide, local debridement of adjacent tissues until the wound bed consists of only healthy, “non-inert”, i.e., living with good blood flow, tissue. Then, both systemic and local antibiotic depots can be used to further treat the patient, mostly for guarding against remaining or new bacteria. Once the tissue bed is clean, a re-implantation of the joint/body part can be performed with hopes that a bacterial infection does not return.
Some procedural difficulties encountered with the aforementioned approach include maintaining the soft tissue envelope during the treatment period. Since there is a loss of axial stability by virtue of removing a joint, the soft tissues can contract and shorten. That in turn, makes the re-implantation process very difficult and risky. If the soft tissue tension can be maintained and, even better, if axial stability with a functional spacer can be used, then the patient minimizes functional loss and re-implantation is facilitated and safer. Furthermore, to minimize the potential for colonization of the intervening spacer, antibiotics can be added to help prevent colonization. Antibiotic bone cement has been used as a treatment of infections for a long time since the work of Bucholz. Since then, there has been developed an antibiotic laden, bone cement as well as products in pre-fabricated shapes that contain a single antibiotic. These existing products contain an aminoglycoside which effectively helps prevent and fight bacterial colonization.
Another method for local antibiotic delivery involves making “beads” or using a powdered, heat stable antibiotic mixed with a common bone cement like poly-methyl-methacrylate (or PMMA), before being formed into small beads on a wire or string. That string of antibiotic beads then gets packed into the wound for eluting high concentrations of antibiotic over time. While effective for infection, that known method provides no limb support for a patient otherwise unable to support their own weight thus rendering such patients wheelchair or bed bound during treatment and recovery.
Another problem previously mentioned is the natural tension of soft tissue to shorten and/or scar a limb. This shortening is difficult to counteract during some re-implantations. There is an increased risk of intra-operative complications and potential neurovascular injury. To deal with this issue, surgeons and manufacturers have created a temporary prosthetic made from an antibiotic laden, bone cement. Representative examples of hip and/or knee implant prosthetics are shown and described in Smith et al U.S. Pat. Nos. 6,155,812 and 6,361,731.
An alternative family of temporary prosthetics is commonly known as a Prostalac® device. For a typical Prostalac hip replacement, a small metal inner core is manually surrounded with antibiotic-laden PMMA. This device provides a metal mold into which a core prosthesis is placed and surrounded with antibiotic laden bone cement. While a surgeon may use the Prostalac for custom blending a preferred recipe of antibiotics, the resultant prosthetic product is cumbersome, expensive to manufacture and rather difficult to use. In any event, a prosthesis is still required and there is little expectation of applicability beyond a simple hip substitution, i.e., those not having extensive proximal femoral bone loss. The same would be true for any intended adaptations of a Prostalac-type system for knee, elbow and/or shoulder replacements (currently not available in the United States).
Yet another alternative to the Prostalac product is a device sold by Tecres as described in Soffiati U.S. Published Application No. 2005/0119756. That device gets delivered to a surgeon pre-fabricated. As such, the antibiotic contents in a Tecres product cannot be modulated, or otherwise customized for a given patient. Due to its limited variety of available sizes, the Tecres knee and hip units do not fit every patient. Nor do they provide axial or rotational stability. This is especially true when a smaller sized stem gets implanted in a larger femoral canal. The attending surgical staff has the option of hand mixing bone cement to manually form a collar (or other adapter over the pre-made Tecres). But such retrofitting takes up valuable staff time and energies, defeating the otherwise beneficial advantages of a system of pre-fabricated parts.
A Biomet® Stage One system, and the somewhat similar process of Ensign et al U.S. Pat. No. 6,942,475, offer disposable knee mold shells, but only the shell parts. Even though these products accomodate custom antibiotic tailoring, they offer limited sizes of knee parts. Their hip component is only intended to replace the femoral neck and head. It uses a standard stem. It is not able to replace diaphyseal parts and only comes in limited sizes for the head. Thus, the options for this system are limited and do not provide for “custom spacers”.
Today's surgeons desire a product that allows for custom fitting for the needs of every implant patient; one that can be expanded in situ (i.e., in the operating room) for accommodating surgical “surprises” like the need to remove additional adjacent bone and/or partially expand a region of the implant for enhancing stability in the canal region. Such a product should be adaptable for making a variety of body part shapes, i.e. for an implant for the ankle, elbow, etc. The method for making such implants from PMMA (or other bone cements) should: (a) enable a wide range of antibiotic recipes, and (b) be cost effective to make and use in situ (i.e. in the operating room itself); so as to lend itself toward ready disposability.
The present device differs from all others in that the sizes for same are templated from non-implanted trials, similar to those used during sizing for joint replacement. Once the patient's size is determined, the corresponding mold is chosen and used to fabricate a cement spacer. Furthermore, by virtue of its modularity, the device can create metaphyseal and diaphyseal components so that greater bone losses can be accommodated. It is unlike the Biomet mold system in that a port is not used. Rather, the present invention introduces cement through an open channel. And while it uses a biocompatible plastic mold that is completely removed and discarded like other products, the molds for this invention are modular and completely customized. This device can be customized in discrete size intervals. It is modular so that if needed, an entire bone segment can be fabricated. In order to maintain strength, an internal steel core can be placed by the surgeon as “rebar” to increase strength. The manufacturing process, materials, and sterilization process all use existing and accepted materials and methods. It will not leach into the mold and does not come into direct contact with the patient. It is much easier to use than other products due to its method of design, and will require a minimum of post-fabrication modifications.
This invention also has potential uses in diaphyseal bone loss cases, i.e., where a segment of bone is lost due to trauma. In such cases, the subsequent layer of tissue surrounding the spacer has living cells that can participate in the subsequent reconstructive process of healing. We are not aware of any other device that provides such modularity, ease of use, and variety of application.